The present invention relates to density measurements of fibrous materials. In particular, this invention relates to a method and device for determining high-speed, real-time, continuous or stationary, in-line, non-invasive, three dimensional multi-point density deviation and density measurements and calculations of yarn, slivers, or pads of non-homogeneous fibrous material, used in the manufacture of feminine hygiene products (i.e., menstrual tampons, pads, and panty liners), as an example, and other fiber based products.
The manufacture of menstrual tampon products is based on the processing of yarn, slivers, or pads of non-homogeneous fibrous material, consisting of some combination of cotton and synthetic and/or cellulosic fibers. Fiber density and moisture content typically vary during the manufacturing process, primarily due to variation in fiber composition. Combining and controlling the proper relative amounts of cotton and synthetic and/or cellulosic fibers in a given tampon manufacturing production line can be accomplished by incorporating high-speed accurate measurement and control of in-line fiber density, moisture content, and temperature.
The main component of tampons is cotton, with synthetic (e.g., viscose rayon, rayon polyacrylates, polyester) and/or cellulosic (e.g., carboxymethol-cellulose) fibers mixed with the cotton to substantially increase the absorbency and anti-wicking properties of tampons. Since the late 1980""s, it has been established through widespread investigation and research, court proceedings (e.g., United States District Court For The District Of Kansas, Case No. 94-1195-FGT), FDA reports and guidelines (e.g., Draft Guidance For The Content Of Pre-market Notifications For Menstrual Tampons, Obstetrics-Gynecology Devices Branch, Office Of Device Evaluation, Center For Devices And Radiological Health, May 25, 1995), that synthetic fibers in tampons are associated with Toxic Shock Syndrome (TSS) and infection in menstrual women. In the case of TSS, the presence of synthetic fibers in tampons has been determined to cause an increase in the production of toxic chemicals in the woman""s body. In the case of infection, the presence of synthetic fibers in tampons inhibits the growth or existence of vaginal flora, due to excessive absorbency of vaginal moisture, necessary for proper vaginal health. Additionally, there are reports that synthetic fibers themselves contain toxins (e.g., xe2x80x9cThe Health Risks of Dioxinxe2x80x9d, an FDA scientist""s report referenced by U.S. congressman Rep. Ted Weiss, at a hearing of the Human and Intergovernmental Relations Subcommittee, Jun. 10, 1992). At that hearing, the FDA concluded that there was dioxin in rayon, and stated that if they (the FDA) did have a problem with medical devices, xe2x80x9cmenstrual products would be the greatest simply because of the mass of the material and the duration of exposurexe2x80x9d. Thus, the potential of tampons causing TSS or infection is directly related to the synthetic fiber content, which in turn, is related to the overall tampon raw material fiber density and moisture content. From this background and information, it is apparent that accurate measure and control of density and moisture content during the manufacture of tampons is important not only from a manufacturing quality control viewpoint, but, also, from a health issue viewpoint.
In the manufacture of products containing fibrous yarn, sliver, or pad raw material, it is desirable to use the fiber density as a primary control parameter, especially in real time, in-line, and continuous mode of operation, in order to maintain product quality assurance (i.e., product composition and performance reproducibility). For a given composition of yarn, sliver, or pad material, fiber density is dependent on its moisture content, and to a lesser extent, dependent upon its temperature. Real time, in-line quality control of the fiber content, of finished feminine hygiene products, for example, is best achieved by measuring and calculating density and moisture deviations and controlling the density and moisture content of the fibrous raw material at both upstream and downstream stages of the manufacturing process.
Prior art devices and methods for measuring fiber density and moisture content are primarily mechanically based, suited for stationary, off-line, and invasive or direct contact operation and analysis of bulk quantities of materials with relatively high densities. Techniques utilizing radiation have been used for density and moisture measurements. Infra-red techniques can be used for moisture determination, but these require direct contact with the material, and are affected by the presence of industrial dust and the focal plane immediately around the sample; Beta rays have been used for density determination, but here there is a health hazard limitation in its application at manufacturing sites. Microwave and other electrical devices and methods for measuring density deviations and density of fibrous materials via moisture and temperature measurements discussed by Kraszewski, A. W. (Microwave Aquametry-Needs and Perspectives, IEEE Transactions On Microwave Theory And Techniques, vol. 39, no. 5, May 1991), provides background and discusses the development of microwave equipment for purposes of electrical monitoring of moisture content in materials. Included there are useful basic definitions, principles, and equations pertaining to microwave analysis of moisture content in materials. At specified material temperature, changes in attenuation and phase-shifts of transmitted microwaves are used for calculating material moisture and density values, respectively.
U.S. patent application Ser. No. 08/974,983, and now U.S. Pat. No. 6,025,724 and Ser. No. 08/777,872, and now U.S. Pat. No. 5,845,529 describe microwave based devices and methods for determining the moisture content of packaged, and non-packaged material, respectively, utilizing various antenna configurations as the source and receiver of transmitted microwave radiation. The earlier of this pair of related patent applications, U.S. patent application Ser. No. 08/777,872, describes moisture content determination of a given module of material (e.g., cotton, paper, processed wood, tea, synthetic fibers). The moisture measuring equipment is aimed at monitoring upstream incoming raw fibrous material, i.e., prior to fibrous material entering the CARD (i.e., fiber separating and processing) machine, and represents a xe2x80x98coarsexe2x80x99 monitoring and analysis of moisture content of upstream incoming fibrous material. As such, the invention is essentially limited to measurement of relatively large (bulk) quantities of minimally processed, high density fibrous material (e.g., typically, 10-15 kilograms per cubic meter), and not highly processed, low density fibrous material (e.g., typically, 4-12 grams per meter, linear density) composed of loose fibers, such as yarn, slivers, or pads (e.g., for tampon production). Moisture content is determined as a function of changes in signal attenuation (amplitude). Compensation of the phase shift for moisture and temperature change is not shown, and there is no discussion pertaining to density deviation measurement or calculation.
U.S. patent application Ser. No. 08/974,983, builds on U.S. patent application Ser. No. 08/777,872, in that compensation for temperature changes of the material, and a method for measurement and calculation of density deviations of indicated material, are included in the invention. A similar, microwave based, dual antenna device is used; phase-shifts and signal attenuation measurements, are used for calculating density and moisture content, respectively. An algorithm was developed to process and maintain the numerical information and data. This invention, too, is essentially limited to measurements of relatively large (bulk) quantities of minimally processed, high density material, and not highly processed, small density fibrous material composed of loose fibers, such as yarn, slivers, or pads. Moreover this invention is specific to providing the method and device of moisture content determination of material wound around a bobbin containing a hollow core. Of these two related patent applications, the more recent one (i.e., U.S. patent application Ser. No. 08/974,983) briefly mentions a form of quality control adjustment of the moisture content of the material, which includes moisture monitoring equipment appropriate for location at an upstream, xe2x80x98coarsexe2x80x99, stage of the fiber based manufacturing process (i.e., pre-CARD fiber separating and processing machine), which can be electronically connected to, and controlled by a central processing unit.
There is thus a widely recognized need for, and it would be highly advantageous to have a highly accurate, high speed, real time, continuous or stationary, in-line, non-invasive, three dimensional, multi-slice method and device for measuring and calculating (small) density deviations, and (low) densities of homogeneous or non-homogeneous fibrous material, at a downstream (fine) stage of production, which includes the capability of compensation for material moisture content and temperature changes, with the object of providing highly accurate, high speed, real-time, continuous or stationary, in-line, non-invasive computerized quality control feedback of critical manufacturing process parameters involved in the production of high quality and high assurance fiber based products (e.g., feminine hygiene products, including menstrual tampons as just one example).
The present invention includes a method and device for highly accurate, high speed, real time, continuous or stationary, in-line, non-invasive, three dimensional, multi-slice density deviation and density measurements and calculations of homogeneous or non-homogeneous fibrous yarn, slivers, or pad material.
The method and device of the present invention enables measurement and calculation of small density deviations and low densities of homogeneous or non-homogeneous fibrous yarn, slivers, or pad material.
The method and device of the present invention also enables highly accurate, high speed, real time, continuous or stationary, in-line, non-invasive computerized quality control feedback of critical manufacturing process parameters involved in the production of high quality and high assurance fiber based (including low density) products.
According to the present invention, there is provided a method for determining the density of a fibrous material, including the steps of (a) introducing the fibrous material into a resonator having a resonance frequency, (b) measuring a shift in the resonance frequency caused by the fibrous material, and (c) inferring the density of the fibrous material from the frequency shift.
According to the present invention, there is provided a device for determining the density of fibrous material, including: (a) a resonator, including an electrically conductive housing defining a cavity, having an input end and an output end, the resonator having a resonance frequency; (b) a tube of low-friction material spanning the cavity from the input end to the output end; and (c) a mechanism for measuring a shift in the resonance frequency caused by the presence of the fibrous material inside the cavity.
According to the present invention, there is provided a device for determining the density of fibrous material, including: (a) a resonator, including: (i) an electrically conductive housing, defining a symmetrical cavity having two substantially identical resonance frequencies with respect to two degenerate modes of microwave radiation, and (ii) a mechanism for perturbing the symmetry, so that the resonator has two distinct resonance frequencies with respect to the two degenerate modes; and (b) a mechanism for measuring a shift in one of the distinct resonance frequencies caused by a presence of the fibrous material inside the cavity.
According to the present invention, there is provided a system for processing fibrous material, including: (a) a CARD machine for separating the fibrous material and reducing the density of the fibrous material; and (b) a mechanism for measuring the density of the fibrous material emerging from the CARD machine, the mechanism including a resonator where through the fibrous material passes.
According to the present invention, there is provided a method for determining highly accurate density profiles of fibrous material used in the manufacture of tampons, leading to improved controllability and quality of the density of the fibrous material, including the steps of: (a) introducing the fibrous material into a resonator having a resonance frequency; (b) measuring a shift in the resonance frequency caused by the fibrous material; and (c) inferring the density of the fibrous material from the shift.
According to the present invention, there is provided a method for determining highly accurate moisture content profiles of fibrous material used in the manufacture of tampons, leading to improved controllability and quality of the moisture content of the fibrous material, including the steps of: (a) introducing the fibrous material into a resonator having a resonator quality; (b) measuring a change in the resonator quality caused by the fibrous material; and (c) inferring the moisture content of the fibrous material from the change in resonator quality.
According to the present invention, there is provided a method for determining highly accurate density profiles of fibrous slivers, leading to improved controllability and quality of the density of the fibrous slivers, including the steps of: (a) introducing the fibrous slivers into a resonator having a resonance frequency; (b) measuring a shift in the resonance frequency caused by the fibrous slivers; and (c) inferring the density of the fibrous slivers from the shift.
According to the present invention, there is provided a method for determining highly accurate moisture content profiles of fibrous slivers, leading to improved controllability and quality of the moisture content of the fibrous slivers, including the steps of: (a) introducing the fibrous slivers into a resonator having a resonator quality; (b) measuring a change in the resonator quality caused by the fibrous slivers; and (c) inferring the moisture content of the fibrous slivers from the change in resonator quality.
The preferred embodiment of the present invention employs a microwave radiation measuring device which operates as a high speed (i.e., micro- to milli-second turn-around-time for measurement, analysis, and processing of each datapoint), multi-slicing (i.e., in-line, continuous mode of operation such that analysis is continuously performed on small, of the order of 2 mm slices of the fibrous material), highly accurate, microwave resonator of non-specific geometry (e.g., cylindrical, coaxial, rectangular), including alternative methods of generating microwave radiation inside the resonator, two cutoff waveguides, a teflon tube for material transport inside the resonator, and components as part of and inside the resonator to correct for imperfections, asymmetry and/or non-homogeneities of the resonator and/or waveguides materials of construction.
The microwave resonator device can operate in at least two alternative modes, including embodiment (a) where the microwave radiation is generated by a broadband microwave generator-synthesizer, and embodiment (b) where the microwave radiation is generated in an oscillator circuit comprising the resonator device (with fibrous material inside of it providing capacitance), and an amplifier with DC power supply. The microwave resonator device in each embodiment is preferably operated for the generation and measurement of resonator resonance frequency shifts (i.e., changes in fr, where fr represents resonator resonance frequency associated with, and measured at, microwaves having maximum amplitude, Am), due to density changes of the analyzed fibrous material.
The device operating in embodiment (a) includes a generator-synthesizer continuously generating a sweeping range of frequencies, controlled by the central processing unit, such that corresponding continuous detection is aimed at identifying microwaves of maximum amplitude, enabling measurement and processing of an array of resonator resonance frequencies, fr, Moreover, due to the electronic set-up of embodiment (a), measurement and processing of a second array is possible, i.e., resonator quality, Q, where Q=fr/(2xcex94f, and xcex94f represents the full width half amplitude bandwidth, evaluated at half-height of the microwave with maximum amplitude, Am/2. In embodiment (a), values of resonator quality, Q, are used as part of a computerized and automatic method for determining moisture content of the fibrous material, which in turn are used to compensate and correct initial calculations of density deviation and density performed by the computer algorithm using resonance frequency shift data. For the device operating as embodiment (a), a separate external moisture content sensor is not needed as part of the overall device of the present invention.
For the device operating in alternative embodiment (b), resonator quality, Q, is not measured, because of the different electronic set-up of the microwave resonator circuit; as such, a separate external moisture content sensor is optionally added to the overall resonator device, thus, enabling compensation and correction of measurements and calculations of density deviation and density by the computer algorithm. For each embodiment, the microwave resonator method and device have the optional capability of measuring and evaluating changes in temperature of the fibrous material, including the addition of a separate external temperature sensor as part of the overall resonator device. Each embodiment of the microwave resonator device has the additional optional capability of providing automatic quality control feedback of critical manufacturing process parameters of the fiber material, including fiber density, moisture content, temperature, and feed rate, at a downstream (fine tune) stage of the overall manufacturing process. For the device operating in embodiment (a), additional components including a heterodyne generator-synthesizer and a signal mixer may be added to the same circuit of the microwave resonator device, in order to provide additional dynamic range, improved sensitivity and accuracy in signal detection, and subsequent enhancement of feedback information sent to the upstream incoming fibrous material processing equipment.
The high speed (i.e., micro- to milli- second turn-around-time for measurement, analysis, calculation, and processing of each data point), multi-slice microwave resonator method and device, including optional capabilities of temperature and moisture content sensors for measurement and calculation, and automatic quality control feedback, are controlled by an in-line central processing unit. The central processing unit contains specially developed algorithms for performing data reduction and calculations from measurements of multi-slice analysis of fibrous materials, based on measurements of the affected microwaves inside the microwave resonator device, including the conversion of frequency shift, resonator quality, and voltage measurements into density deviation, average density, moisture content, and temperature. Values of density deviation and average density, and optionally, moisture content and/or temperature, as functions of time, are numerically and/or graphically displayed on an in-line computerized display unit. The combination of the central processing unit, which includes electronic components for (A/D) digital signal processing, and a computerized display unit, provides a variety of electronic storage and manipulation, including hardcopy printouts of desired measurements, calculations, numerical data and/or graphs.
The computer algorithm, especially written for multi-slice (i.e., of the fibrous material) data reduction, calculations of the various measurements, and generating values of density deviation, average density, and optionally, moisture content, is preferably (i.e., as in embodiment (a)) based on two principle arrays: 1) microwave resonator resonance frequency, fr, and 2) signal (resonator) quality, Q. Material density and moisture content are directly proportional to these arrays, respectively, whereby appropriate functions and equations are used for performing the necessary calculations. Actual values of fiber material density, used for in-line processing purposes, are evaluated, in part, from empirical functions, data of which is contained in calibration graphs of resonance frequency, fr, vs density, and resonator quality, Q, vs density, for a variety of fibrous materials at known temperature and moisture content, recorded under off-line, controlled calibration conditions. In embodiment (a), improved accuracy in final density calculations is gained, if desired, by compensating initial calculations of the density for material moisture content, material structure (i.e., shape, type), and temperature. Moisture content is evaluated from measurements and calculations of resonator quality; functions of material structure are evaluated from employing the resonator device at standard conditions, and for various well characterized shapes and types of fibers; and temperature is evaluated from an appropriately located external temperature sensor near the entrance to the resonator device.
For embodiment (b), multi-slice data reduction,calculations of the various measurements, and generating values of density deviation, average density, and optionally, moisture content, is based on one principle array, i.e., microwave resonator resonance frequency, fr. As in embodiment (a), material density is directly proportional to this array, whereby appropriate functions and equations are used for performing the necessary calculations. Actual values of fiber material density are evaluated, in part, from empirical functions, data of which is contained in calibration graphs of resonance frequency, fr, vs density, for a variety of fibrous materials at known temperature and moisture content, recorded under off-line, controlled calibration conditions. In this embodiment, improved accuracy in final density calculations is gained, if desired, by compensating initial calculations of the density for material moisture content, material structure (i.e., shape and type), and temperature. However, in this embodiment, values of moisture content are obtained from actual measurements, taken from an optional externally located moisture content sensor. Final, compensated values of material density, as in embodiment (a), require the use of empirical functions of material structure, and temperature, where material temperature is evaluated from the external temperature sensor located near the entrance to the resonator device.
Physical location of the microwave resonator device with respect to the overall fiber based manufacturing process is between equipment used for upstream (coarse) handling and processing of incoming raw fibrous material, including a CARD fiber separating machine, and downstream (fine) processing equipment involved in further processing the separated fibrous material into finished products. Information provided by the microwave resonator device to the central processing unit represents xe2x80x98fine tuningxe2x80x99 capability of fiber processing parameters critical to downstream stages of the overall production process, whereas, moisture/density monitoring equipment situated upstream of the fiber separating CARD machine represents xe2x80x98coarse tuningxe2x80x99 capability of fiber processing parameters critical to fibrous material entering the CARD machine, and serves as an xe2x80x98alarmxe2x80x99 of large, erratic, or otherwise undesirable density deviations occurring early in the production process. Location of the resonator device of this invention is well suited for high speed, in-line quality control feedback of various incoming raw fibrous material characteristics, including density, moisture content, and temperature; and process parameters, including incoming material feed rate, and momentum of the CARD machine cylinders.
The embodiments of the present invention allow the capability of design modification according to the exact type of application, depending upon such factors as type, size, and density of the fibrous material, as well as the exact nature of the overall manufacturing process of a particular fiber based finished product.
Novelty and advantage of the present invention over prior art devices and methods for density measurement of fibrous material is based on its ability to monitor, measure, and calculate in real time (i.e., synchronization between all device components), density (and optionally, moisture content and orientation of the fibrous material) deviations in continuous or stationary, in-line, and non-invasive mode of operation with high accuracy and high speed. Moreover, the method and device are applicable to three dimensional, multi-slice measurement and analysis of fibrous materials. In order to emphasis the advantage of the ability of the device in the present invention to perform real time, multi-slice analysis, an actual xe2x80x98workingxe2x80x99 illustration of this device follows: For a typical, continuous mode of operation, fibrous pad speed of 1200 meter/min=20 meter/sec=20 millimeter/millisecond, this device is capable of measuring, recording, and processing measurements at a rate of one datapoint (i.e., one slice) every 0.1 millisecond; thus, each recorded data point (slice) represents 2.0 mm of fibrous pad material, being supplied during the manufacture of tampon products. Turnaround data processing time, i.e., time from initial measurement to the time of feedback control action, and sample size provided here as an example, give an idea of the rapidity and accuracy the quality control feedback loop this device is capable of during actual manufacturing of tampons, for example, and other textile products.
Another important advantage of the method and device of the present invention, absent from the prior art, is its applicability to measurement and analysis of small density deviations and to low (linear) density fibrous materials, such as yarn, slivers (e.g., 4-5 grams per meter) and pad (e.g., 11-12 grams per meter), used in the manufacture of tampons. Preferred location of the resonator device of the present invention is at a strategic point of fine adjust to the overall manufacturing process, i.e., downstream from the CARD fiber separating and processing machine.
Another advantage of the present invention is that density measurements are corrected for moisture content, and temperature changes of the fibrous material, during real time, continuous or stationary, in-line, non-invasive, three dimensional, and multi-slice mode of operation.
An additional novelty of the present invention is its ability to likewise, provide automatic quality control feedback. A practical example of the utility of the automatic quality control feedback during the manufacturing process occurs when feedback control triggers automatic adjustment of process parameters such as a) incoming raw material feed rate, b) momentum of fiber processing equipment cylinders (i.e., of the CARD machine), and c) raw material humidity and air temperature, enabling better control of moisture level and ultimately density of the finished fiber based product. Moreover, the device of the present invention is advantageously used in a complementary way to devices of prior art, in that the resonator device of this invention is preferably used for fine tuning quality control, whereas, microwave monitoring devices of above referenced patent applications are preferably used for coarse tuning quality control, with respect to a given overall fiber based manufacturing process.